the sample mass is increased. This results from both the formation of a non-linear adsorption isotherm and the increased elution strength of the mobile phase in contact with the benzene. In fact, as a result of solute–solute interaction the benzene is, in effect, partially eluting itself. The effect of the mass overload of benzene on the other solutes is also clearly demonstrated. The presence of the high concentration of benzene in the mobile phase increases the elution rate of both the naphthalene and the anthracene. Its also seen, however, that the effect of the high concentration of the benzene on the closer eluting peak naphthalene is to produce band dispersion, whereas the anthracene band does not suffer significant dispersion and the retention of both the front and the rear of the anthracene peak appear to be linearly reduced with sample mass. The  chromatograms shown in figure 7 also show that the anthracene peak maintains its symmetry throughout all sample sizes. The

In a similar manner and under identical conditions Scott and Kucera examined the effect of naphthalene over load (from 1.1 to 19.1 mg) on the retention of benzene, naphthalene and anthracene. The results are shown in figure 9.   After J. Chromatogr., Ref. (3)   Figure 9. The Effect of Mass Overload of Naphthalene on the Retention of Benzene, Naphthalene and Anthracene

be obtained. Notwithstanding, the results unambiguously demonstrate the advantages of column overload. In the chromatograms on the left hand side of figure 3, 10 ml, 1 ml, 2 ml, and 3 ml of sample was placed on the column each containing 176 mg of benzene, 9 mg of naphthalene and 0.3 mg of anthracene. So all the samples contained the same mass of each  solute. It is seen that a sample volume of 3 ml (theoretical value calculated from equation (2), was 3.1 ml) just allows benzene and naphthalene to be separated

Similarly, in the chromatograms shown on the right hand side of figure 3, 2, 4 and 6 ml of a solution each containing 9.0 mg of naphthalene was injected onto the column and. The maximum sample volume that just permits the separation of naphthalene and anthracene, identified experimentally was 6 ml (theoretical value calculated from equation 2 was 6.1 ml). Destefano and Beachel (4) has also investigated the effect of volume and mass overload on resolution. They concluded that, given the choice, it is advantageous to overload a column with a large volume of a dilute solution of sample, as an alternative to using a small

overload experiments as that employed in the volume overload experiment. In the investigation of mass over load, the sample volume was kept constant at 200 ml, and a mixture of benzene, toluene and anthracene was placed on the column, the mass of benzene being increased progressively from 180 mg to 16.9  mg. An example of three of the chromatograms obtained are shown in figure 7. A chromatogram of the reference sample is shown on the left of figure 7 and contained 180 mg of benzene, 9 mg of naphthalene and 0.3 mg of anthracene. The mass of naphthalene and anthracene was kept at 9.0 mg and 0.3 mg respectively for all samples so only the benzene was overloaded. The mass of benzene was increased to 8.1 mg and then to 16.9 mg. Simple visual inspection of the chromatograms indicate that as the mass of solute is increased, the benzene peak has broadened, and become asymmetrical, which will be a direct result of the adsorption isotherm entering the non-linear region. The peak distortion

nbsp; It is also seen that up to 16 mg of benzene could be injected onto the column before the peak merged into that of naphthalene. In fact, by sacrificing a small amount of benzene significantly more benzene (probably at least 30 mg) could have been injected before the major portion of the peak was contaminated with naphthalene. This compromise, which involves sacrificing a small quantity of the selected component to obtain a larger load, is common in preparative chromatography, and arises from the tailing that again results from the formation of a non-linear adsorption isotherm. In samples where the two